Method and regulating system for applying defined actuating forces

ABSTRACT

The present invention relates to a process and a control system for generating defined actuating forces in a brake which is electrically operable by way of an actuator, wherein there is a first static relation between the brake&#39;s actuating travel and the actuating force. The process and the control system permit determining the actuating forces which develop during operation without additional sensors. To achieve this object, according to the present invention, a second relation which corresponds to the operation of the brake is determined from the first relation and an information which represents the variations of the first relation.

TECHNICAL FIELD

The present invention relates generally to vehicle brakes and moreparticularly to a process and a control system for generating definedactuating forces in a brake which is electrically operable by way of anactuator.

BACKGROUND OF THE INVENTION

International patent application WO 96/033010 discloses a disc brakewhich is preferably operable by way of an electric motor-and a reductiongear. The special features of the prior art brake include that the rotorof the electric motor has an annular design and embraces the reductiongear radially. These provisions achieve that the axial overall length ofthe actuating unit is greatly shortened. However, the above-mentionedpublication does not indicate how defined actuating forces can begenerated during operation of the prior art brake.

There is a defined relation between the actuating travel X_(Bet), bywhich the brake pads are pressed against the brake disc, and theactuating force F_(Bet) generated. This relation can be modeled withsufficient accuracy by a mathematical model, for example, in the way ofa static characteristic curve F_(Bet)(X_(Bet)). If this relation isknown with sufficient accuracy, the actuating or displacement travelwhich corresponds to a desired actuating force and, in consideration ofthe gear reduction, the corresponding actuator position can bepredetermined (nominal position value) and approached in a positionallycontrolled manner. This procedure corresponds to a control of theactuating force, i.e., there is an open action sequence (no sensorfeedback) with respect to this physical quantity.

On the other hand, it is also possible to reconstruct the currentactuating force due to the actuator position which is easily availableunder measuring technology aspects and is therefore known, by way of aparametric or non-parametric model. However, the clearance position mustadditionally be known in both cases. The quality of this control,exactly as the reconstruction (calculation) of the actuating force fromthe position signals of the actuator, depends on the model quality ofthe process (in this case: the characteristic curve). Because thecharacteristic curve under review in the operation of the brake issubject to certain significant changes, mainly due to temperature andwear, it is necessary to make an adaptation of this characteristic curveto the current condition of the brake in defined intervals. Thisadaptation must be effected on the basis of internal signals which arealready provided in the electric brake system. This obviates the needfor additional external sensor means (no direct measurement of theactuating force). From this results as a demand placed on themathematical model for the electromechanically operable brake that itdescribes the behavior under review sufficiently precisely and that thesignals used must comprise the desired information on the actuatingforce.

An object of the present invention is to propose a process and a controlsystem which permit determining the actuating forces that develop duringoperation. Also, such determination be effected especially without theuse of additional sensors.

In terms of process, this object is achieved because a second relationwhich corresponds to the operation of the brake is determined from thefirst relation and an information which represents variations of thefirst relation.

To specify the idea of the present invention, the informationrepresenting the variations of the first relation is determined byevaluation of signals which occur during braking operation, inparticular, in a displacement travel of a static characteristic curverepresenting the first relation or in an extension or compression of thestatic characteristic curve which represents the first relation. Thesignals preferably represent the position of the actuator and thecurrent value to be sent to the actuator.

In a preferred aspect of the subject matter of the present invention,the speed or the acceleration of the actuator is additionallydetermined.

Also, it is especially favorable that the second relation is determinedaccording to the formula

F_(Bet) =f(X_(Bet))=λf· _(Basis)(X_(Bet)−X_(V))  (1)

wherein

f_(Basis) is the first relation,

λ is an extension or compression factor,

X_(Bet) is the actuating travel of the brake, and

X_(V) is the displacement travel.

In another favorable feature of the present invention, a mathematicalmodel of the brake which comprises the first relation is used whereinthe portion of the current being supplied to the actuator, the saidportion corresponding to the actuating force, is taken into account todetermine both the extension or compression factor and the displacementtravel by way of a parameter estimation process.

The established values of the extension or compression factor and of thedisplacement travel are checked for plausibility preferably before theyare employed, and the parameter estimation process is monitored by usingthe signal representative of the speed of the actuator.

Therefore, the disclosed process of a model-based reconstruction of theactuating force focuses on the modeling of condition-induced variationsof the basic characteristic curve (basis characteristic curve) and themethods of determining the adaptation parameters on the basis ofinternal actuator and brake signals. The latter signals are of majorsignificance and provide the basis of a most accurate metering of theactuating force on the basis of internal actuator signals.

When using the updated static characteristic curve for the metering ofthe actuating force, principally two procedures are possible which willbe reviewed in detail hereinbelow. Preferably, the actuating force as afunction of the actuating travel is taken into consideration because inthis case it is only necessary to consider the effective rigidity of theentire system and the condition-responsive variations thereof.

A control system according to the present invention for implementing theabove-mentioned process distinguishes by the following provisions:

a) a position controller to which the control difference between anominal actuator position and signals representative of the actualactuator position is sent as an input signal, and connected downstreamof which controller is an electronic servo booster having an outputsignal which actuates the actuator,

b) a characteristic curve adaptation and adaptation monitoring module towhich the output signal of the servo booster and the signalrepresentative of the actual actuator position are sent as inputquantities, and which furnishes an information about variations of thefirst relation which occur during operation of the brake,

c) and the information is sent to a performance graph module whichcalculates actuating travel nominal values from actuating force nominalvalues in consideration of the variation information, and connecteddownstream of which module is a conversion module which calculates thesignals representative of the nominal actuator position from theactuating travel nominal values.

A second variation of the control system for implementing the process ofthe present invention includes the provision of

a) a deceleration controller to which the control difference betweensignals representative of an actuating force nominal value and anactuating force actual value is sent as an input signal, and connecteddownstream of which controller is an electronic servo booster having anoutput signal which actuates the actuator,

b) a characteristic curve adaptation and adaptation monitoring module towhich the output signal of the servo booster and the signalrepresentative of the actual actuator position are sent as inputquantities, and which furnishes an information about variations of thefirst relation which occur during operation of the brake, on the onehand, and a signal representative of the actuating travel actual value,on the other hand, which signals

c) are sent to a performance graph module which calculates actuatingforce actual values from the actuating travel actual values inconsideration of the variation information.

The conversion module preferably represents a mathematical model of agear that acts between the actuator and the brake. Besides, theinformation about variations of the first relation, which occur duringoperation of the brake, can be sent to the deceleration controller toupdate said's parameters.

When the brake is installed in an automotive vehicle it is especiallyappropriate that an information representative of the rotational speedof the automotive vehicle wheel is sent to the characteristic curveadaptation and adaptation monitoring module.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first configuration of a control circuit for implementingthe process of the present invention.

FIG. 2 is a second configuration of a control circuit for implementingthe process of the present invention in a representation whichcorresponds to FIG. 1.

FIG. 3 is a diagram which illustrates the mode of function of theperformance graph module shown in FIG. 2.

FIG. 4 is a flow chart which illustrates the mode of function of theperformance graph adaptation and monitoring module shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The control system illustrated in FIG. 1 is configured to convert thedeceleration signal (in this case: preferably actuating forceF_(Bet,Soll)) (signaled by the driver or predetermined by a superiorfunction unit) into a corresponding nominal position value by means ofan inverse characteristic curve stored in memory (actuating forcecontrol). The characteristic curve is updated by way of a mathematicalmodel for the electromechanic brake including a model for thecondition-responsive variation of the characteristic curve on the basisof actuator signal sensor means which is easily accessible using currentmeasuring technology. The control system shown generally comprises aposition controller 1 and an electronic servo booster 2 connecteddownstream of the position controller 1. The output signal I_(M) of thebooster is used to actuate an actuator 3 (indicated only schematically)of an electromechanically operable brake which is designated byreference numeral 4. The actuator 3 is preferably equipped with anangular position measuring system 5 whose output signal that isrepresentative of the actuator actual position is sent to the servobooster 2, on the one hand, and to a position signal conditioningcircuit 6, on the other hand. The output signal q_(A,Ist) of theposition signal conditioning circuit 6 is sent to a summation point 7,which is connected upstream of the position controller 1, on the onehand, and together with the signal I_(M) is sent to a characteristiccurve adaptation and adaptation monitoring module 8, on the other hand,wherein in addition the adaptation is monitored and the establishedadaptation parameters are checked for plausibility in order to increasethe reliability. In the summation point 7, a deviation Δq which is usedas an input quantity of the position controller 1, is produced from asignal representative of an actuator nominal position q_(A,Soll) and theabove-mentioned signal q_(A,Ist). The signal q_(A,Soll) is preferablyproduced by a gear module 9 which takes into consideration the behaviorof a reduction gear (not shown) that is interposed in terms of effectbetween the actuator 3 and the brake 4. Connected upstream of the gearmodule 9 is a performance graph module 10 in which is stored an inversestatic characteristic curve f (F_(Bet,Soll)) of the partial systemactuator 3—brake 4 and in which a signal F_(Bet,Soll), which representsan actuating force nominal value that is predetermined, for example, bythe driver of an automotive vehicle equipped with the above-mentionedbrake or by a superior function unit, is converted into an actuatingtravel nominal value X_(Bet,Soll) under the influence of thecharacteristic curve adaptation and adaptation monitoring module 8. Theparameters X_(V) and λ which influence the conversion run in theperformance graph module 10 and are furnished by the characteristiccurve adaptation and adaptation monitoring module 8 provide aninformation about variations which occur during operation of the brake 4with respect to the relation between the brake's actuating travel X andits actuating force F. X_(V) refers to the shift of the basischaracteristic curve in the direction ±X_(bet) and λ refers to theextension or compression factor of the mentioned characteristic curve.

An important characteristic feature of the control system shown in FIG.2 is the reconstruction of the deceleration wish signal (hereinpreferred: actuating force) from the measured position information bymeans of a memorized and updated characteristic curve for the actuatingforce control, as well as a characteristic curve adaptation andadaptation monitoring module which is generally based on actuator signalsensor means and mathematical models. A deceleration controller 11 isused in the control system shown instead of the position controller 1mentioned with respect to the FIG. 1 embodiment. In all other respects,the circuit arrangement corresponds largely to the circuit diagram shownin FIG. 1. Connected downstream of the characteristic curve adaptationand adaptation monitoring module 14 which, in addition to theabove-mentioned parameters X_(V), λ, still furnishes a signalcorresponding to an actuating travel actual value X_(Bet,Ist) is aperformance graph module 12 in which a static characteristic curvef(X_(Bet,Ist)) of the actuator-wheel brake assembly is stored. Theoutput value F_(Bet,Ist) of the module 12 is sent to a summation point13 wherein a deviation ΔF that serves as an input quantity of thedeceleration controller 11 is produced from the signal representing theabove-mentioned actuating force nominal value F_(Bet,Soll) and thesignal F_(Bet,Ist). The signal representing the actuating force nominalvalue F_(Bet,Soll) is again predetermined (as in the arrangementaccording to FIG. 1), for example by the driver of an automotive vehicleequipped with the above-mentioned brake, or a superior function unit. Inthe performance graph module 12, the signal X_(Bet,Ist) which representsthe actuating travel actual value is converted into an actuating forceactual value F_(Bet,Ist) under the influence of the characteristic curveadaptation and adaptation monitoring module 14.

The following comments will be given on the static characteristic curveshown in FIG. 3 and referred to hereinabove.

A desired actuating force may be achieved by a defined displacement ofthe brake pads in relation to the brake disc. Therefore, the behavior ofthe process under review is generally identical to that of a springsystem with a variable spring rigidity K_(E) and can be modeled withsufficient accuracy by a static characteristic curve for the actuatingforce F_(Bet) as a function of the actuating travel X_(Bet):

F_(Bet)=K_(E)(X_(Bet))•X_(Bet), for X_(Bet)>0, otherwise 0  (2)

The fundamental behavior of the electric brake is shown by a staticforce-travel characteristic curve, e.g., corresponding to equation (2).The curve may be depicted, for example, by significant pairs of pointsin a table with a certain number of support points. The division neednot absolutely be equidistant. Intermediate points of this table arecalculated online during braking operations by linear interpolation orextrapolation. Apart from the description by a non-parametric model inthe above-mentioned fashion, other description modes, e.g., by aparametric model, are also possible. The characteristic curve whichprevails in the form of a table represents a basis characteristic curve(index B or basis) and represents the static behavior of the electricbrake in its ‘normal condition’. Condition-responsive variations of thischaracteristic curve, generally by heating up and wear, must be sensedand adapted in the course of operation of the brake. It shall be assumedthat the behavior formulated by the basis characteristic curve cannotprincipally be changed by condition-responsive variations of the staticbehavior of the brake and can be depicted by the following modificationsof the basis characteristic curve:

shift of the basis characteristic curve by X_(v) in the direction±X_(Bet) and/or

extension or compression of the shifted basis characteristic curve by afactor R.

The presently available characteristic curve can be generated by thismodel set-up from the basis characteristic curve corresponding toequation (1). The main object now involves determining the adaptationparameters in the current braking operation and thereby achievingupdating of the static characteristic curve.

The basis for the method of reconstruction shown in FIG. 4 is theactuator position, which in general can be measured easily, and thebasis characteristic curve which is updated continuously or whenrequired by way of a corresponding model set-up with the aid of theinternal actuator signals.

Following the recording of the actuator signals I_(M) and q_(A,Ist) (seefunction block 100) is the determination of the signals which correspondto the actuator speed and acceleration (see function block 200).

Prior to the determination of the adaptation parameters, it is checkedby way of the direction of movement of the actuator whether theactuating force information can be detected in the actuator current inthe present movement condition of the actuator and whether it is safelypossible to determine the adaptation parameters based on actuatorsignals for updating the basis characteristic curve (see function block300).

When the identification ability is detected, a condition estimation ofI_(M,Bet) (see function block 400) will follow. A basis characteristiccurve F_(Bet,B)(X_(Bet)) memorized point-by-point for the electric brakeis under review for this purpose so that, with the position X_(Bet)known, an estimated value for the actuating force in the ‘normalcondition’ can be determined by linear interpolation by way of the basischaracteristic curve:

{circumflex over (F)}_(Bet,B) =m _(B)(i)·X_(Bet) +b _(B)(i).

wherein m_(B) is the rigidity of the entire system in the interval underreview,

b_(B) is a force offset value, and

i is the interval under review.

Equation (3) indicates the resultant actuating force with a defineddisplacement travel for the case that the present behavior of theelectric brake exactly corresponds to that one of the basischaracteristic curve. Condition-responsive variations of thischaracteristic curve are taken into account on the basis of theprovisions shown in FIG. 3. The condition-responsive variations of thestatic behavior of the actuator-brake group are plotted by the followingmodification of the basis characteristic curve:

{circumflex over (F)}_(Bet) =λ•m _(B)(i) •X_(Bet) +b _(B)(i)λ•m_(B)(i)•X_(V)

The generation of an actuating force F_(Bet) for the brake via the gearsystem stresses the actuator (in general: I_(M,Bet)) For example, whenthe actuator is an electric motor, this force causes a load torque. Theactuator current I_(M) is exactly so great that the load forces(generally friction and load by the actuating force) which act on theactuator can be compensated, and the actuator including the coupledmechanics accelerates to the commanded speed. (There is a defined(known) relation characterizing the actuator between the actuatorcurrent and the actuator force/torque which produces the actuatormovement. This relation is linear in many cases.) In this configuration,the full information about load forces or torques which counteract theactuator, especially about the generated actuating force, is thereforecomprised in the actuator current or actuator force or torque in thisconfiguration.

The condition estimation of I_(M,Bet) (see function block 300) iseffected by way of the measured actuator signals with the aid of aninterference signal observer, based on a mathematical model for theelectromechanic drive train of the electric brake. It should be takeninto account that the reconstructed signal I_(M,Bet) represents both theloading of the actuator by the actuating force F_(Bet) and the increasein friction in the electromechanic drive train which is due to thisloading.

When the brake is applied, the actuator must work counteracting theloading and in opposition to the mechanical efficiency so that theinformation about the actuating force is in any case contained andsignificantly identifiable in the actuator current. Therefore, adetermination of the adaptation parameters to update the force-travelcharacteristic curve by way of the actuator signals is possible when thebrake is applied. When the brake is released, there is the possibility(especially in the presence of a poor mechanical efficiency) that theinformation is no longer significantly identifiable in the current.Updating of the characteristic curve cannot be performed in this casewhen the brake is released.

To identify the parameters X and X_(V) on the basis of the reconstructedsignal I_(M,Bet) in consideration of equation (4), a recursive ornon-recursive parameter estimation process known from prior artliterature may be used which is generally based on minimizing aquadratic quality criterion (see function block 500). Because virtuallyknown methods are employed in this respect, there is no need for adetailed consideration of the parameter estimation process hereinbelow.When employing the parameter estimation, care should be taken that anidentification of the parameters being sought is ensured and that theidentification can supply reasonable results only if the parameters aresufficiently excited by the signals.

Further, it is appropriate to check the estimated parameters forplausibility (see function block 600) and, only after the availabilityof plausible adaptation parameters is confirmed, to release theseparameters also as up-to-date parameters (see function block 700).Otherwise, the old parameters may be maintained (see function block800).

The reconstruction of the actuating force is performed according toequation (4) by way of the basis characteristic curve and inconsideration of the adaptation parameters identified on the basis ofthe actuator signal sensor means (see item 12, FIG. 2).

If an identification ability is not detected, further model parametersof the electric brake can be updated as the requirements may be (seefunction block 900), and the relevant parameters of the preceding stepcan be maintained (see function block 800) in the determination ofF_(Bet) (see item 12, FIG. 2).

What is claimed is:
 1. Process of generating defined actuating forces bywhich brake pads are pressed against a brake disc, in a brake which iselectrically operable by way of an actuator, wherein there is a firststatic relation between the brake's actuating travel, and the actuatingforce of the brake generated by the actuator, and the first staticrelation is depicted by a mathematical model, comprising the step of:deriving a second relation which corresponds to the operation of thebrake, wherein said second relation is determined from the firstrelation and information which represents variations of the firstrelation determining the information representing the variations of thefirst relation by evaluating signals which occur during operation of thebrake further including the signals which occur during operation of thebrake to represent the position of the actuator and the current value tobe sent to the actuator.
 2. Process as claimed in claim 1, furtherincluding defining the information which represents the variations ofthe first relation is a characteristic curve which illustrates extensionor compression.
 3. Process as claimed in claim 1, further includingdetermining the speed or the acceleration of the actuator.
 4. Process asclaimed in claim 1, defining the information which represents thevariations of the first relation as a displacement travel (X_(V)) of ashifted static characteristic curve which represents the first relation.5. Process as claimed in claim 4, wherein the second relation isdetermined according to the formula F_(Bet) =f(X_(Bet))=λ·f _(Basis)(X_(Bet)−X_(V)) wherein f_(Basis) is the first relation, λ is anextension or compression factor, X_(Bet) is the actuating travel of thebrake, and X_(V) is the displacement travel.
 6. Process as claimed inclaim 1, using the speed or the acceleration of the actuator todetermine the portion of the current being supplied to the actuator,wherein said portion corresponding to the actuating force.
 7. Process asclaimed in claim 6, checking the established values of the extension orcompression factor and of the displacement travel for plausibilitybefore they are employed.
 8. Process as claimed in claim 6, furtherincluding monitoring the parameter estimation process by using thesignal representative of the speed of the actuator.
 9. Control systemfor generating defined actuating forces by which brake pads are pressedagainst a brake disc, in a brake which is electrically operable by wayof an actuator, wherein there is a first static relation between thebrake's actuating travel, which has to be covered for application of thebrake pads against the brake disc, and the actuating force of the brakegenerated by the actuator, and the first static relation is depicted bya mathematical model, comprising: a) a position controller to which thecontrol difference between a nominal actuator position and signalsrepresentative of the actual actuator position is sent as an inputsignal, and connected downstream of which controller is an electronicservo booster having an output signal which actuates the actuator, b) acharacteristic curve adaption and adaption monitoring module, to whichthe output signal of the servo booster and the signal representative ofthe actual actuator position are sent as input quantities, and whichfurnishes an information about variations of the first relation whichoccur during operation of the brake, c) a performance graph module forreceiving said information and calculating actuating travel nominalvalues from actuating force nominal values in consideration of thevariation information, and connected downstream of which module is aconversion module which calculates signals representative of the nominalactuator position from the actuating travel nominal values.
 10. Controlsystem as claimed in 9, wherein the conversion module represents amathematical model of a gear that acts between the actuator and thebrake.
 11. Control system for generating defined actuating forces in abrake which is electrically operable by way of an actuator, whereinthere is a first static relation between the brake's actuating traveland the actuating force, comprising: a) a deceleration controller towhich the control difference between signals representative of anactuating force nominal value and an actuating force actual value issent as an input signal, and connected downstream of which controller isan electronic servo booster having an output signal which actuates theactuator, b) a characteristic curve adaption and adaption monitoringmodule to which the output signal of the servo booster and the signalrepresentative of the actual actuator position are sent as inputquantities, and which furnishes an information about variations of thefirst relation which occur during operation of the brake, on the onehand, and a signal representative of the actuating travel actual value,on the other hand, which c) are sent to a performance graph module whichcalculates actuating force actual values from actuating travel actualvalues in consideration of the variation information.
 12. Control systemas claimed in claim 11, wherein the information about variations of thefirst relation, which occur during operation of the brake, are sent tothe deceleration controller to update said's parameters.
 13. Controlsystem as claimed in claim 11, wherein the brake is installed in anautomotive vehicle, and wherein an information representative of therotational speed of the automotive vehicle wheel is sent to thecharacteristic curve adaption and adaption monitoring module. 14.Process of generating defined actuating forces by which brake pads arepressed against a brake disc, in a brake which is electrically operableby way of an actuator, wherein there is a first static relation betweenthe brake's actuating travel, and the actuating force of the brakegenerated by the actuator, and the first static relation is depicted bya mathematical model, comprising the step of: deriving a second relationwhich corresponds to the operation of the brake, wherein said secondrelation is determined from the first relation and information whichrepresents variations of the first relation defining the informationwhich represents the variations of the first relation as a displacementtravel (X_(V)) of a shifted static characteristic curve which representsthe first relation.
 15. Process of generating defined actuating forcesby which brake pads are pressed against a brake disc, in a brake whichis electrically operable by way of an actuator, wherein there is a firststatic relation between the brake's actuating travel, and the actuatingforce of the brake generated by the actuator, and the first staticrelation is depicted by a mathematical model, comprising the step of:deriving a second relation which corresponds to the operation of thebrake, wherein said second relation is determined from the firstrelation and information which represents variations of the firstrelation defining the information which represents the variations of thefirst relation is a characteristic curve which illustrates extension orcompression.